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Expanding the lower range of the vortex flowmeter must start with reducing the interference signal
2012-3-7 9:08:36

Installation of vortex flowmeter

只能单向测量,安装时注意保证介质流量方向与流量计箭头所示方向一致。 1. The vortex flowmeter can only measure in one direction. When installing, pay attention to ensure that the medium flow direction is consistent with the direction shown by the arrow of the flowmeter. 2. The best installation method of vortex flowmeter is vertical installation, the medium passes through the flowmeter from bottom to top. That is, the flow meter is installed on a vertical pipe, and the flow direction is from bottom to top. 3. For horizontal installation, the flow meter must be installed in the high-pressure area of the entire system and the corresponding outlet pressure must be ensured; do not install at the highest point of the pipeline, because the highest point often has gas accumulation and the pipeline is not full; the outlet cannot be vented directly. 4. When measuring high-temperature fluids, try to use a vertical installation method; if you have to install it horizontally, please install the transmitter part of the flowmeter vertically downward or horizontally to avoid the temperature being too high; pay attention to the air flow at the installation location Or well ventilated. 5. Straight pipe section requirements: At least 15 times the pipe diameter in front of the flowmeter and 5 times the pipe diameter after the flowmeter are guaranteed. If there are interference sources such as elbows, indentations, and expansions in front of the flowmeter, you must ensure that the pipe diameter is 30-40 times in front of the flowmeter and 6 times in diameter after the flowmeter. The flow meter should be installed upstream of the regulating valve, pressure or temperature sensor. 6. Note that the diameter of the pipeline should be slightly larger than or equal to the internal diameter of the instrument during installation. 7. When using a sealing ring, note that the inner diameter of the sealing ring should be slightly larger than or equal to the inner diameter of the meter, and the center of the sealing ring is located in the center of the pipe. When the cable inlet is used to seal the electrical connection of the instrument, attention must be paid to the seal of the cable entry hole. The corresponding sealed interface (M20 × 1.5; 1/2 ”NPT; G1 / 2”) must be selected according to the meter cable entry model, and installed correctly and tightly. Without sealing joints or sloppy installation, the sealing effect cannot be achieved, which is one of the most common causes of instrument damage.

How to solve the anti-interference of vortex flowmeter
是基于卡门涡街原理而研制成功的一种具有国际先进水平的新型流量计。 The vortex flowmeter produced by Jinhu Dongxiang Instrument Co., Ltd. is a new type of internationally advanced flowmeter developed based on the Carmen vortex street principle. Because it has the advantages of other flowmeters, among many flow detection solutions, vortex flowmeters have high measurement accuracy, small pressure loss, easy installation, and are not affected by the physical properties of the measured medium. Characteristics such as transmission, application technology is becoming more and more perfect, especially in large pipe diameter and water, oil and other liquid media flow measurement applications are more widely used.
In order for the vortex flowmeter to measure as low a flow velocity and a small flow as possible, the signal-to-noise ratio must be increased, that is, the amplitude of the effective flow signal should be increased as much as possible to reduce the amplitude of the mechanical vibration interference signal. Improving the structure shape of the fluid-impedance, so that the sensor can better receive the pulsating pressure of the vortex, and the effective signal amplitude can be increased. But a more effective method is to package two corresponding piezoelectric crystals on both sides of the vortex generator, that is, using a differential piezoelectric sensor and a differential amplifier circuit. Since the mechanical vibration forces on the two piezoelectric crystals are the same, and the fluid vortex is alternately generated on both sides of the fluid resistance, after differential amplification, the same mechanical vibration signals of the two piezoelectric crystals cancel and reduce each other. 2 The opposite flow signals of the bulk piezoelectric crystals are added and enhanced. Thus, the interference of mechanical vibration signals is greatly reduced.
The vortex flowmeter's obstructing fluid uses a piezoelectric crystal to detect the vortex frequency. The piezoelectric signal is amplified by an AC and a trigger to change the vortex frequency into a pulse signal. The pulse signal is sent to the secondary meter and the measured flow rate is displayed after conversion. Among them, the amplification factor K of the AC amplifier and the threshold voltage of the trigger can be adjusted.
In order for the threshold voltage to block the interference signal and to ensure that the trigger can output a valid signal, the interference signal V must be less than the threshold voltage u, and the effective signal voltage E is greater than the threshold voltage u, that is, the working condition of the vortex flowmeter is: E> u > V The magnitude of the interference signal V determines the lower range limit of the vortex flowmeter. Therefore, expanding the lower range of the vortex flowmeter must start with reducing the interference signal. Adjusting the AC amplification factor K can only strengthen the output signal, but the lower limit of the range cannot be extended. Electromagnetic interference and mechanical vibration interference are important interference factors of the vortex flowmeter, which limits the decrease of the range and affects the Use in flow measurement. By designing optical isolation current-limiting anti-interference measures on the circuit, it can effectively solve the interference of the ground current and the main problem of anti-electromagnetic interference; the structural design uses differential piezoelectric sensors and differential amplifier circuits of dual piezoelectric crystals Can eliminate the interference of mechanical vibration. 的量程下限扩展至原量程下限的1/2~1/3。 As a result of the above two anti-interference measures, the lower limit of the range of the vortex flowmeter can be extended to 1/2 to 1/3 of the lower limit of the original range.